Apparatus for plotting contour maps automatically employing a cathode ray tube



March 12, 1968 M. M) BIRNBAUM ET AL 3,372,615

APPARATUS FOR PLOTTING CONTOUR MAPS AUTOMATICALLY EMPLOYING A CATHODE RAY TUBE Filed March 28, 1963 v Sheets-Sheet 5 FIG.6

M. 3,372,615 APPARATUS FOR PLOTTYING CONTOUR MAPS AUTOMATICALLY March 12, 1968 M. BIRNBAUM ET A EMPLOYING A CATHODE RAY TUBE Filed March 28, 1963 I '7 Sheets-Sheet 6 FIGTB- FIG.7A

FIG.9

March 12, 1968 M. BlRNBAUM ET AL 3,372,615

APPARATUS FOR PLOTTING CONTOUR MAPS AUTOMATICALLY EMPLOYING A CATHODE RAY TUBE Filed March 28, 1963 7 sheets-sh et 7 United States Patent 3,372,615 APPARATUS FUR PLOTTING CONTOUR MAPS AUTOMATICALLY EMPLOYING A CATHODE RAY TUBE Morris M. Birubaum, Pasadena, Le Roy J. Ridenour,

Burbank, and Phil M. Salomon, Sunland, Califl, assignors to General Precision Systems Inc, a corporation of Delaware Filed Mar. 25, 1963, Ser. No. 268,302 10 Claims. (CI. 88-14) The present invention relates to apparatus for the production of topographic maps of the type exhibiting contour lines which represent points of equal altitude in nature. More particularly the present invention relates to apparatus for producing such maps automatically from oriented, stereoscopically related diapositive photographs, i.e. photographs of the same terrain taken from different points of equal altitude. In apparatus of this type the oriented diapositives may be scanned in synchronism with rays of light that may diverge from a common point source at a selected distance from the diapositives and which are focused into points upon the diapositives by suitably placed lenses; and identical photosensitive devices are arranged behind the diapositives to register the variations in light as the two rays are swept across the diapositives. When the scanning light points pass through unrelated spots in the two diapositives, they are modulated to ditferent degrees, i.e., their intensity is usually reduced in different degrees by the densities of the developed photographic layers at the two spots where they pass through the diapositives at the moment. However, when they pass through spots in the diapositives corresponding to one and the same spot in nature they are modulated in an identical, or nearly identical, manner because corresponding spots in the two diapositives have approximately the same degree of opaqueness. Hence, whenever in the process of scanning the two diapositives in synchronism, the two searching light points are modulated to an identical extent, this may be indicative of the fact that they have encountered a spot in nature that is located at a level corresponding to the altitude represented by the distance between the level of the oriented diapositives and the common point of origin of the two searching light points. Hence, whenever during the scanning process the two photosensitive devices behind the diapositives register identical or nearly identical responses, this may indicate that the correlated points of light have encountered corresponding spots in the diapositives that depict a spot in nature which has the altitude represented by the distance between the point of origin of the light rays and the level of the scanned diapositives.

To visually represent discovered points of a desired contour, another cathode ray tube may be employed and its electron beam may be swept across its phosphor screen in synchronism with the electron beam which produces the point source of light by means of which the diapositives are scanned; and whenever the scanning points of light encounter corresponding spots in the diapositives, i.e. spots that depict one and the same spot in nature, the resultant identity in the output signals of the photosensitive devices is employed to apply a voltage to a control grid of the second cathode ray tube, which increases (or decreases) the strength of the electron beam of said second tube and in this manner displays the discovered spot of the desired contour visually upon the phosphor screen of "ice said second tube. Thus, by sweeping the scanning light points over the oriented diapositives in a succession of closely adjacent parallel paths, consecutive points of the desired contour may be visually displayed upon the phosphor screen of the display tube and depict the desired contour thereon.

The ditficulty with apparatus of the type described is that the light points in sweeping over the oriented diapositives may simultaneously encounter spots of accidentally identical light permeability which do not depict one and the same spot in nature, and the apparatus may therefore display spots on the screen of the display tube, which are not part of the desired contour.

Broadly, it is an object of our invention to minimize the possibility of such spurious responses in automatic contour plotting apparatus of the type defined above.

Our invention is based upon the concept that spurious responses due to accidentical similarity in the light permeability of spots, 011 the diapositives, which the scanning light points may encounter simultaneously and which are otherwise unrelated, are far less likely to occur if the scanning light points, once they have encountered the desired contour, are constrained to follow the discovered contour rather than discover it anew with every consecutive sweep.

Accordingly, it is another object of'the invention to provide a control arrangement for contour plotting apparatus of the type referred to, that is effective to hold the electron beam of the scanning tube in its momentary position of deflection once the light points focused upon the diapositives have encountered related points on the diapositives which depict a point of the desired contour.

More particularly, it is an object of the invention to provide a control arrangement of the type referred to, that operates to maintain and/ or return the electron beam of the scanning tube continually to a position wherein the light points focused upon the diapositives rest upon corre' sponding spots of the diapositives which represent a point of the desired contour, if and when an effort is made to move the electron beam away from the discovered contour.

When measures are provided to restore the electron beam of the scanning tube continually to a position where the points of light focused upon the diapositivesrest upon related spots, forced movement of the beam in approximately the direction of the contour will cause the beam to follow the contour precisely; and by applying the same control voltages to the display tube as operated upon the scanning tube, the beam of said display tube may be caused to trace the desired contour in a continuous line upon the phosphor screen thereof rather than in a succession of individual spots of which every one must be rediscovered.

The means generally available in cathode ray tubes for forcing the electron beam to sweep across the phosphor screen of the tube permit the beam usually to be moved along a horizontal axis and/or along a vertical axis of the screen. It is obvious what has been said above, that in causing the electron beam of the scanning display tube to follow a discovered contour and in this manner trace the discovered contour visibly upon the screen of the display tube, it is desirable to know the directional trend of the contour; to be more specific, it is desirable to know whether the discovered contour extends closer to the horizontal or the vertical axis of the scanning screen and even whether it is closer to one or the other axis in i the positive or in the negative direction, because it is obvious that the most dependable results may be obtained by forcing the beam of the scanning tube in the proper direction and allowing the control arrangement of the invention to return the points of light to corresponding spots of the contour on the two diapositives over the shortest possible distance.

It is yet another object of our invetion, therefore, to provide a control arrangement for contour plotting apparatus of the type referred to, that senses the directional trend of a discovered contour.

Furthermore, it is an object of our invention to provide a control arrangement which senses the directional trends of a discovered contour and controls the means for forcing the scanning beam in one or the other direction across the scanning screen in such a manner that the beam is forced in the direction closest to the trend of the discovered contour.

More specifically, it is an object of our invention to provide a control arrangement for contour plotting apparatus of the type referred to, (1) which is effective, once a contour has been discovered, to restore the electron beam of the scanning tube continually to a position wherein the scanning light points pass through related spots of the diapositives which depict a point of the desired contour, (2) which senses the directional trend of the desired contour as viewed from the discovered contour point and (3) which unbalances the electron beam position restoring operations in such a manner that the beam is forced to move in the direction of the contour.

These and other objects of our invention will be apparent from the following description of the accompanying drawings which illustrate a preferred embodiment thereof and wherein:

FIGURE 1 is a block diagram of a contour plotting arrangement embodying our invention.

FIGURES 2, 3, 4 and 5 are more detailed diagrams of some of the component units of the arrangement represented by the block diagram of FIGURE 1.

FIGURE 6 is a diagram illustrating the manner in which the output signals of the two photomultiplier tubes comprised in the apparatus of our invention are processed to make it easier to compare them electronically.

FIGURES 7A and 7B are diagrams illustrating schematically rosettes traced upon the phosphor screen of the scanning tube comprised in the apparatus of our invention.

FIGURE 8 is a diagram illustrating the ability of rosettes such as shown in FIGURE 7 to sense discrepancies on the diapositives between apparent representations of a point in nature, that are displaced in the direction of I the x-axis.

FIGURE 9 is a diagram similar to FIGURE 8 illustrating the improved performance of a modified rosette pattern; and

FIGURES 10 and 11 are reproductions of contour maps produced with the apparatus of the invention.

Having first reference to FIGURE 1, the apparatus of the invention comprises a scanning unit A wherein two oriented stereoscopically related diapositives 10a and 10b may be scanned in synchronism by points of light produced by bundles of light rays that originate from a common point source of light indicated at 12 and which are focused upon the diapositives by suitably placed lenses 14a and 14b, respectively. The point source of light 12 is produced by impingement of an electron beam 15 generated by the cathode 16 of a cathode ray tube 18 upon the phosphor screen 20 thereof. The photocathodes of two photomultiplier tubes 22a and 22b placed behind the diapositives 10a and 10b, respectively, receive the light rays upon passage through the diapositives causing said tubes to produce output signals that vary in proportion to the modulation to which the rays of light are subjected as they pass through the diapositives.

The apparatus of the invention also comprises a unit B which produces currents that are delivered to sets of deflection coils 24x and 24y associated with the cathode ray tube 18 of unit A to cause the electron beam thereof to trace a rosette pattern upon the screen 20. Additionally, the apparatus of the invention comprises a unit C that supplies voltages which may be applied to another set of deflection coils 2 6x and 26y associated with cathode ray tube 18 to shift the electron beam 15 either along the x or the y-axis of a Cartesian system across the screen of the tube 18 so that the points of light focused upon the diapositives 10a and 10b may be made to search said diapositives along an x or y-axis thereof.

Likewise comprised in the apparatus of the invention is a correlation unit D wherein the varying outputs of the two multiplier tubes 22a and 22b of unit A are compared to ascertain phases of identity in their trends, that are of suflicient duration to indicate that the scanning points of light in sweeping over the diapositives 10a and 10b have encountered and/or are located on related areas in said diapositives, that depict one and the same area in nature.

Wherever unit D has found such identity between the outputs of the photomultiplier tubes 22a and 22b, it supplies a signal to a display unit E which is formed by another cathode ray tube 28. Said tube is provided with sets of deflection coils 30x and 30y corresponding to the deflection coils 26x and 26y of the scanning unit A, and said coils 30x and 30y are controlled from unit C to move the electron beam 32 generated by the cathode 34 of tube 28 in unison with the electron beam 15 of unit A. Any signal supplied by the corelation unit D, which is indicative of the fact that a point in the desired contour has been found, is applied to a control grid 36 of tube 28 to increase the intensity of its electron beam to an extent where it produces a bright spot upon the screen 38 of the tube, and thus depicts visibly a point of the desired contour on said screen.

The apparatus of the invention includes also a unit F, which comprises a system I that processes the output of the rosette generating unit B and the correlation unit D, as operation of unit B sweeps the light points over the diapositives 10a and 10b in a rosette pattern across and about a discovered point of the desired contour, to produce servo voltages as the searching light points approach, or withdraw from, the desired contour. When these servo voltages are applied to the deflection coils 26x and 26y they are effective to maintain the centers of the light rosettes precisely upon corresponding points of the desired contour on the two diapositives. In addition, unit F encompasses a system identified as section II which processes the output of the rosette generating unit B and the correlation unit D to sense the direction in which the desired contour extends. Said system II interferes with, and unbalances, the application of the above mentioned servo voltages to the deflection coils 26x and 26y of tube 18 in such a manner that the centers of the light rosettes focused upon the diapositives follow the desired contour; and since the servo voltages produced by unit F are applied to the deflection coils 30x and 30y of the display tube 28 in the same unbalanced manner, the electron beam 32 of said tube traces the desired contour visibly upon the screen 38 thereof. Unit F comprises also a system designated as section III which regulates the application of the various control voltages generated by unit C and sections I and II of unit F to the deflection coils 26x, 26y and 30x, 30y of the cathode ray tubes 18 and 28, respectively, so that they cannot interfere with each other.

As pointed out hereinbefore, unit B controls the supply of currents to the deflection coils 24x and 24y of tube 18 in such a manner as to cause the electron beam 15 thereof to trace continually a rosette pattern upon the screen 20 of said tube. As explained in US. Patent No. 3,175,121, issued on March 23, 1965, for an Arrangement for Deflecting the Electron Beam of a Cathode Ray Tube, a rosette is determined by the following two equations in the Cartesian system:

'wherein the factor a determines the diameter of the rosettes and the factor n. represents the number of the rosette petals. To satisfy these equations we multiply a sine wave signal of a predetermined frequency with a sine wave signal of a higher frequency and convert the resultant product voltages into a Varying deflection field extending across the electron beam of the cathode ray tube 18 in a predetermined direction, and simultaneously We multiply a sine wave signal of said higher frequency with a cosine wave signal of said predetermined frequency and convert the resultant product voltages into a second deflection field extending across the electron beam at substantially right :angles to said first field.

Having reference to FIGURE 2, the block 413 represents a generator set to generate a sine wave signal of a predetermined frequency and the block 42 represents a generator set to generate a sine wave signal of a higher frequency. The output of generator is first passed through two parallel phase shift networks represented by the blocks 44 and 46 respectively. Network 44 is arranged to shift the signal by 45 in the plus direction and network 46 is arranged to shift the signal by 45 in the minus direction. Hence, the signals emerging from the phase shift networks 44 and 46 have a phase difference of 90 and are therefore related in the manner of -a sine wave signal and a cosine wave signal. The signal emerging from phase shift network 46 may therefore be regarded as a sin signal and the signal emerging from phase shift network 44 as a cos signal. The output of phase shift network 44 and the unchanged output of generator 42 are both applied to a voltage multiplier represented by the block 48 and the output of phase shift network 46 and the unchanged output of generator 42 are both supplied to a voltage multiplier represented by the block 50. Multipliers of the type required for multiplying high frequency signals have been described in US. Patent No. 3,215,825, issued Nov. 2, 1965, for a Multiplier Circuit, to which reference is made for a detailed description.

The voltages emerging from multiplier 50 constitute the product sin 12 sin 5. They are delivered to a suitable driver stage represented by the block 52y that controls the current flow through the deflection coils 24y which are located at opposite points on the neck of tube 18 along what may be regarded as the y-axis of screen 20. On the other hand, the voltages emerging from multiplier 48 represent the product sin 11 cos and are delivered to a suitable driver stage represented by the block 52x which controls the current flow through the deflection coils 24:: located at opposite points of the neck of tube 18 along the x-axis of its screen 26. The resultant deflection fields affect the electron beam 15 of cathode ray tube 18 in such a manner that it traces a rosette upon the phosphor screen of tube 18 as illustrated in FIGURES 7A and 7B.

As pointed out hereinbefore, the unit C makes it possible to shift the rosette tracing electron beam 15 across the screen of tube 18, in the direction of an x or y-axis thereof. It possesses a source of positive voltage represented by the block p and a source of negative voltage represented by the block 6011. By means of a manually operable single-pole double-throw switch 64 either a positive voltage or a negative voltage may be applied through an initially open gate 66 and an integrator 68 in section III of unit F to a driver stage 70x which passes such currents through the deflection coils 26x of the scanning tube 18 and the deflection coils 30x of the display tube 23 as will shift the electron beams of said tubes to the right or the left, respectively, of the y-axis of their screens, and similarly another manually operable single-pole, doublethrow switch '74 may be set to apply either a positive or a negative voltage through an initially open gate 76 and an integrator 78 in section III of unit F to a driver stage 80y which passes such currents through the deflection coils 26y of scanning tube 18 and the deflection coils 30y of display tube 28 as will cause the electron beams of said tubes to shift across the screens thereof in an upward or downward direction above or below the x-axis of said screens. As a result of the described movements of the electron beam of scanning tube 18 and the consequent movement of the point source of light 12 produced by the beam on the screen of said tube, the points of light focused upon the diapositives by lenses 14a and 14b scan the diapositives in synchronism along the x or y-axes thereof, as the case may be, and in the process are bound to encounter the desired contour; and when they do, the outputs of the photo multiplier tubes 22a and 22b become increasingly similar and eventually identical causing the correlation unit D to produce an output signal which is applied to, and blocks, the initially open gates 66 and 76 through a line 81 to terminate manual control of the deflection of the electron beams 15 and 32 of the scanning tube and the display tube respectively. From this moment on unit F takes over control of the position of said beams.

The correlation unit D (FIGURE 3) is similar to, and may be identical with the correlation arrangement described in US. Patent No. 3,114,831, issued Dec. 17, 1963, for a Correlation Circuit. As disclosed in said patent application the signals tobe compared, i.e. the output signals of photo multiplier tubes 22a and 22b, which are of the character illustrated at a and b in FIG- URE 6, are first converted into forms in which it is easy to compare them electronically for similarities in their trends. To this end any variations in the trends of the signals in positive or negative direction are converted into positive and negative rectangular valve pulses of equal amplitude irrespective of the amplitude and steepness of these variations, but of different duration depending upon where a change in the direction of the signals occurred and how long the new trend lasted. The resultant sequences of positive and negative square wave pulses of equal amplitude but varying location and duration are shown in FIGURE 6 as lines A and B respectively, in super-position upon signals a and b, and are easy to compare electronically. Circuitry for converting signals of the type shown at a and b into the series of square wave pulses A and B, respectively, are illustrated and described in the above mentioned US. Patent No. 3,114,831 to which reference is made for details.

Reverting to FIGURES 1 and 3, the outputs of photo multiplier tubes 22a and 22b are amplified in suitable video amplifiers represented by the blocks 82a and 8212, are passed through band pass filters represented by the blocks 84a and 84b, and are then converted into sequences of square wave pulses of equal amplitude but varying polarity and duration in circuitries represented by the blocks 86a and 86b respectively. As likewise explained in the repeatedly mentioned US. Patent No. 3,114,831, each signal is now divided into its positive and negative half. For this purpose the series of pulses representing signal a are applied to a pair of parallel polarity sensing gates 88p and 8811 of which gate 88p is arranged to pass positive pulses only and gate 8811 is arranged to pass negative pulses only. Similarly, the series of pulses representing signal b are applied to a pair of parallel polarity sensors 90p and 9011 of which sensor 90 passes positive pulses only and sensor 91in passes negative pulses only. The positive halves of the two converted signals A and B are now compared in an And gate represented by the block 92a which produces an output only during the time interval while two pulses appear simultaneously at its input side; and the pulse signals representing the negative halves of the converted signals are similarly compared in an And gate 92b. Gates 92a and 92b represent the actual correlation system which produces an output only when the compared signals display areas of identity. The outputs of correlation gates 92a and 92b are both delivered to a common integrator represented by the block 94, but the output of correlation gate 92b is first inverted in an inverter stage represented by the block 96 so that it may be of the same polarity as the output of correlation gate 92a. While the gates 92a and 92b can not produce output pulses at the same time because they respond to the simultaneous occurrence of positive pulses or negative pulses in the same two signals and neither of these signals can exhibit a positive and negative pulse at the same instant, we prefer to pass the outputs of correlator gates 92a and 92b through an Or gate represented by the block 98 before delivering them to integrator 94. This Or gate functions as an isolating stage.

The integrator 94 is arranged to integrate the voltages delivered thereto over constant time intervals of substantial duration. Thus, whenever the scanning light points in unit A are moved over the oriented diapositives 10a and 10b by manipulation of unit C, and pass over unrelated areas of said diapositives, any spurious similarities in the trends of the signals produced by the photo multiplier tubes 22a and 22b do not significantly change the average output of integrator 94, provided the integrator intervals are sufliciently long. When the scanning light points pass over truly related areas, however, and the signals produced by the photo multiplier tubes become increasingly similar, the correlation gates 92a and/or 92b pass a multitude of pulses which build up in integrator 94 and produce a pronounced increase in the integrator output, that is known as a correlation excess. Such a correlation excess indicates that the scanning light points have encountered a point of the desired contour of the terrain depicted on the diapositives.

T indicate this contour point visibly, the output of correlator 94 is passed through a DC. amplifier 100 and applied to the hereinbefore mentioned control grid 36 of the display tube 28 in unit E to increase the intensity of the electron beam of said tube to an extent whereat it produces a bright point upon the phosphor screen of said tube, and since the electron beam of display tube 28 is moved by the deflection fields generated in coils 30x and 30y in synchronism with movement of the electron beam of the scanning tube 18 as effected by manipulation of unit C, the point of light appearing on the screen of display tube 28 is in congruence with the point source of light on the screen of the scanning tube and is therefore truly representative of a point of the desired contour. To make sure that the output of integrator 94 may reach the control grid of the display tube only when it is large enough to leave no doubt that the scanning light points on the diapositives a and 10b have encountered a contour of the desired altitude, a threshold circuit may be interposed between amplifier 100 and control grid 36, as indicated by the block 102.

As mentioned hereinbefore, the appearance of an output from correlation unit D closes the normally open search control gates 66 and 76 through line 81 (FIGURE 1) so that any further manipulation of unit C remains without effect upon the position of the electron beams of the two cathode ray tubes. The hereinbefore mentioned integrators 68 and 78 which are controlled by the gates 66 and 76, are of the type having a very long discharge time, and by virtue of the charges built up in said integrators prior to closure of the gates 66 and 76, the beams of the two cathode ray tubes remain for the moment in the state of deflection in which they were when the light rosette centers encountered the desired contour. It is now unit F and especially its section I and II that take over control of the deflection of the electron beams in the two cathode ray tubes, and said unit operates to effect such variations in the deflection of said beams as will cause them to trace the desired contour in one or the other direction upon the phosphor screens of their tubes.

Unit F comprises means collectively identified as section I that sense departure of the scanning light points from corresponding spots of the discovered contour on the two diapositives and which develop correctional voltages that when applied to the deflection coils of the scanning tube, restore the electron beam thereof to a position wherein the centers of the light rosettes are again located precisely upon said corresponding contour spots; and when this condition is established, the correctional voltages developed and applied to the deflection coils of the scanning tube as the scanning light points sweep in a rosette pattern about said spots and thus continually withdraw from and return to positions of precise coincidence with said corresponding spots on the diapositives, balance each other out so that the centers of the light rosettes would ordinarily remain upon said spots. Unit F, however, comprises also means collectively identified as section II which sense the trend of the discovered contour, i.e. whether the contour extends closer to the x or the yaxis and Whether the closest approach between the desired contour and one or the other of said axes exists in a positive or negative direction; and in accordance with our invention said contour trend sensing means is arranged to block application, to the deflection coils of the cathode ray tubes, of the correctional voltages which would tend to move the rosette centers in a direction away from closest proximity with the desired contour if they were allowed to act upon the deflection coils by themselves. As a result thereof, the correctional voltages which would ordinarily maintain the rosette centers upon the initially established contour spots on the two diapositives, are thrown out of balance, and the correctional voltages developed as the light points trace petals upon the diapositives in the area through which the discovered contour takes its course, become effective to shift the electron beam of the scanning tube unopposedly in the general direction of the desired contour.

To establish the above described performance, unit F contains means that ascertain which of the petals of the rosette traced by the electron beam of the scanning tube upon the phosphor screen of said tube produces maximum correlation as obviously the desired contour must lie in the direction of these particular petals and it is obviously the coincidence of these petals with the desired contour that produces phases of maximum correlation. The rosetteproducin g output of the multipliers 48 and 50 of unit B is, therefore, not only applied to the deflection coils 24x and 24y of the scanning tube 18, but also to an array of gates that divide the voltages into their positive and negative components depending upon whether they are the voltages that deflect the beam to the right or left of the y-axis or above or below the x-axis. Having specific reference to FIGURES 1 and 4, the current produced by driver stage 52x of unit B is passed through an amplifier x and applied to two parallel polarity detectors 112p and 11211 of which detector 112p is arranged to pass positive voltages only and detector 112n is arranged to pass negative voltages only; and similarly the output of driver stage 52y is passed through an amplifier 110y and applied to two parallel polarity detectors 114p and 11411 of which detector 114p is arranged to pass positive voltages only and detector 1l4n is arranged to pass negative voltages only. Placed into the output line of each of said polarity detectors is a gate 118p, 118n, 120p and 120n, respectively. These gates are normally closed, but are arranged to be opened temporarily when correlation indicating pulses are supplied by the correlation gate arrangement 92a, 92b of unit D. In FIGURES l, 3 and 4, a line 121 commencing at a point between the Or gate 98 and integrator 94 of unit D applies all correlation pulses simultaneously to each of the gates 118p, 118n, 120p and 12011 so that they may pass signals emerging from polarity detectors 112p, 112n, 114p and 11411, whenever correlation exists between the output signals of the photo multiplier tubes 22a and 22b. While the correlation indicating pulses are applied to all four gates 118p, 118n, 120p and 120n simultaneously, it must be borne in mind that only one of each pair of the polarity detectors 112 11222 and 114;), 11411, respectively, is capable of supplymg an output at one time because the same signal is ap 9 plied to the detectors of each pair, and one and the same signal cannot be both positive and negative at the same time. Hence, at any particular instant when correlation exists between the output signals of the photomultiplier tubes, a signal can emerge only from gate 118p or gate 11811, and from gate 120p or gate 12011.

Let us reflect for a moment what the appearance of signals in two of the output lines of the two pairs of twin gates 118p, 11811 and 120p, 12011 means in reality. If gate 118p passes a signal, it means that correlation exists as the point source of light on the screen of scanning tube 18 causes petals to be traced upon the dia-positives :to the right of the y-axis of the rosettes (FIGURE 7). On the other hand if a signal appears in the output line of gate 11811, it means that correlation exists when the point source of light causes light petals to be traced upon the diapositives to the left of the y-axis of the rosettes. Similarly, if a signal emerges from gate 120p, this means that correlation exists when the point source of light traces petals upon the diapositives above the x-axis of the rosettes; and if a signal appears in the output line of gate 12011, this means that correlation exists when the points of light trace petals upon the diapositives in the area below the x-axis of the rosettes. Thus, for instance, if a preponderance of signals appears in the output lines of gates 118p and 12011, this means that the area of greatest correlation lies in the sector to the right of the y-axis and below the x-axis of the rosettes traced upon the diapositives at the moment. If the centers of the rosettes are displaced from corresponding segments of the desired contour on the diapositives, the outputs of gates 118?, 11811, 120p and 12011 indicate in which direction truly correlated spots of the desired contour lie on the diapositives and in which direction the light-source-producing electron beam of tube 18 has to be moved to establish precise coincidence of the rosette centers with said corresponding spots of the desired contour.

The gates 118p, 11811, 120p and 12011 are of the type which pass the signals received from their associated polarity detectors without changing the signal amplitude, and in accordance with the invention the outputs of said gates are delivered as servo voltages through the integrators 68 and 78 to the driver stages 70x and 80x, respectively, to cause said stages to pass such correctional currents through the deflection coils 2.6x and 263 of the scanning tube 18 as will move the centers of the light rosettes into precise registry with corresponding spots of the desired contour on the two diapositives; and since the driver stages 70x and 80y do not only control the named deflection coils of the scanning tube but also the deflection coils of the display tube, said servo voltages will simultaneously effect such deflections of the electron beam of the display tube as will precisely locate a point of the desired contour on the phosphor screen 38 of said tube. Having reference to FIGURES 1, 4 and the output of gates 118p and 118n is delivered to the integrator 68 through twin lines 122p and 12211 which are drawn heavier than other connections shown in FIGURES 4 and 5 for reasons of clarity. Similarly the output of gates 120p and 12011 is delivered to the integrator 78 through heavily drawn twin lines 126p and 12611. In FIGURES 4 and 5 the lines 122p and 12211 are shown to pass through normally open inhibiting gates 124p and 12411, respectively, whose significance will presently appear, and isolating stages 140p and 14011; and lines 126p and 12611 are shown to pass through normally open inhibiting gates 128p and 12811 and isolating stages 148p and 14811.

Whenever the rosettes of light are properly centered upon corresponding segments of the desired contour on the diapositives, the effects of any correctional voltages emerging from gates 118p, 11811, 1200 or 12011 upon the deflection fields established by the coils 26x and/or 26y cancel each other out as pointed out hereinbefore so that the beams of the scanning tube and the display tube ret'ain their particular state of deflection. To trace the desired contour upon the display tube, however, it is necessary that the scanning beam be shifted in the direction of the contour. Both the scanning tube and the display tube possess means in the form of the repeatedly mentioned deflection coils 26x, 26y and 30x, 30y, respectively, for shifting the beam along the x and y-axes of a Cartesian system, and along both said axes the beams may be shifted either in the positive or the negative direction depending upon the polarity of the deflection currents passed through said coils. In operating the system of our invention to trace a desired contour on the screen of the display tube, it is of advantage to shift the beam of the scanning tube along the axis and in the direction which is closest to the actual course of the contour, and let the described beam-position-correcting arrangement of the invention adjust the position of the beam along the other axis continuously in such a manner as will locate the rosette'centers precisely upon the proper contour line. The arrangement of the invention therefore comprises means for sensing the trend of the desired contour as viewed from the center point of the rosettes, and for effecting movement of the electron beam of the scanning tube and of the display tube along the axis and in the direction that lies closest to the contour.

Let it be recalled that gate 118p passes pulses whenever correlation exists between the output signals of the photomultiplier tubes 22a and 2211 as the scanning light points trace petals upon the diapositives to the right or East of the y-axis of the rosettes, and gate 11811 passes pulses whenever correlation exists as the scanning light points trace petals upon the diapositives to the left or West of the y-axis of the rosettes. Analogically, gates p and 12011 pass pulses whenever correlation exists as the scanning light points trace petals upon the diapositives above and below, i.e. to the North or South" of the x-axis of the rosettes respectively. Let it also be remembered that pulses cannot emerge from 118p and 1 1811 at the same time because said gates are arranged to pass positive and negative pulses of the same deflection signal, and one and the same signal cannot have positive and negative pulses at the same moment. For the same reason it is impossible for pulses to emerge from gates 120p and 12011 at the same time. To determine whether the desired contour extends closer to the x or the y-axis of a Cartesian system, the outputs of gates 118p and 11811 are both applied as positive voltages to an integrator 142 and the outputs of gates 120p and 12011 are applied as negative voltages to said integrator 142. For this purpose the negative output of gate 11811 is passed through an inverter 144 before it is applied to the integrator 142 and analogically the positive output of gate 120p is passed through an inverter 146 before it is delivered to the integrator 142. For reasons that will appear hereinafter, the combined outputs of gates 118p and 118n pass through a normally ineflective attenuating gate 141x before they reach the integrator 142 and the combined outputs of gates 120p and 12011 pass through a normally ineffective attenuation gate 141 before they reach said integrator 142.

If the contour upon which the searching light rosettes are located, extends closer to the x-axis of the rosettes than the y-axis thereof as illustrated at 145 in FIGURE 7A, the pulses emerging from gate 118p will be larger than the pulses emerging from gate 120p, and the pulses emerging from gate 11811 will be larger than the pulses emerging from gate 12011. This occurs because each voltage detector passes signals proportional to the rosetteoreating signals generated by unit B. Gates 118p and 11811 receive signals from the x-axis driver and amplifier 5211 of unit B, namely, x=a sin 11 cos /1. These signals pass through the plus voltage detector 112p when they are plus, and through the minus voltage detector 11211 when they are minus. In a similar manner, gates 120p and 12011 receive signals from the y-axis driver and amplifier 52y of unit B, namely, y=a sin n sin 5.

As pointed out hereinbefore, each of the gates 118, 1, 11811, 120p and 12011 are constructed to pass signals with their amplitude preserved when they are rendered conductive by a correlation pulse arriving from correlation unit D through line 121. When the contour being sensed lies close to the x-axis, the signals passing through the x-axis sensing detectors 118p and 11811 will be larger than those arriving through the y-axis sensing detectors 120p and 12011, because in this situation the x component of the rosette (x-=a sin 11 cos is much larger than the y component of the rosette (y=a sin 11 sin e). Gate 118p passes the plus portions of sin 11 cos and gate 120 passes the plus portions of sin 11 sin Since the rosette isscanning along or close to the x-axis. at this moment, cos 5 is much larger than sin 45, and gate 118 puts out pulses of much larger amplitude than gate 12011. When the positive-going pulse output of gate 118p is of much larger amplitude than the positive-going pulse output of gate 120p, the result will be a remainder of positive ,voltage from gate 1 18p, and the integrator 142 will therefore produce a positive output.

On the other hand, if the contour clings more closely to the y-axis of the rosette, as represented by line 147 in FIGURE 7B, pulses of larger amplitude will emerge from .gate 120p and gate 12011 than from gates 118p and 11811,

respectively, and the output of the integrator will be negative. Hence, the polarity of the output of integrator 142 is indicative of whether the desired contour extends closer to the x-axis or the y-axis of the rosettes. The output of the axis-selecting integrator 142 is, therefore, applied to a polarity sensing network comprised of two parallel detectors 150p and 150n. Detector 150p is arranged to pass positive voltages but blocks negative voltages, and detector 15011 is arranged to pass negative voltages but blocks positive voltages. A voltage emerging from detector 150;) indicates that the desired contour extends closer to the x-axis of the light rosettes traced upon the diapositives. A signal emerging from detector 15012, on the other hand, indicates that the desired contour extends closer to the y-axis of the rosettes than to the x-axis thereof.

For the arrangement of the invention to give best performance, it is not only necessary, however, to sense whether the desired contour extends closer to the x or the y-axis of the scanning rosettes, it is desirable also to sense whether a greater approach between an axis and the desired contour occurs in the plus or minus direction or to express it in more colloquial terms, in the eastern or western direction if the contour is found to extend close to the x-axis, or in the northern or the southern direction if the contour is found to run in the proximity of the y-axis.

To determine whether the desired contour extends closer to the x-axis of the light rosettes traced upon the diapositives, in eastern or western direction, the output of gate 118p and the uninverted output of gate 11811 are applied to another integrator represented by the block 154x in FIGURE 5, and if the output of said integrator is positive, this is indicative of the fact that more correlation exists when the scanning points of light trace rosette petals upon the diapositives to the right of the v y-axis of the rosettes than when they trace petals to the left of said y-axis. This means that the desired contour follows the x-axis of the rosettes more closely in an eastern direction than in the western direction as illustrated by line 145 in FIGURE 7A. On the other hand if the output of integrator 154x is negative, this means that it is the side on the left of the y-axis, i.e. the western side, whereat the desired contour extends closer to the x-axis of the rosettes. In accordance with our invention the output of integrator 154x is, therefore, applied 'to a polarity sensing network composed of two parallel detectors 156E and 156W which are arranged to pass only positive and negative voltages, respectively. An output of detector 156E means that the desired contour extends closer to the x-axis of the rosetted in the positive or eastern direction (FIGURE 7A), and an output of detector 156W means that it is closer to the x-axis in the negative or western direction.

Similarly, the uninverted output of gate and the output of gate 12011 are delivered to an integrator 1543 and the output of said integrator is applied to a polarity sensing network composed of parallel detectors 156N and 1568. An output from detector 156N indicates that the contour is closer to the y-axis in the positive or northern direction, as illustrated by line 147 in FIGURE 7B, and an output from detector 1568 indicates that the contour is closer to the y-axis in a negative or southern" direction.

Let us now revert to the twin lines 122p, 12211 and 126p, 12611, which are drawn in heavier lines than the other connections in FIGURES 4 and 5, and which deliver such servo-voltages to the control integrators 68 and 78, respectively, of the deflection coils 26x and 26y of the scanning tube as will return the beam of said tube to a position wherein the light rosettes are centered upon corresponding points of the contour in the diapositives. As pointed out hereinbefore said lines contain normally open gates 124p, 12411, 128p and 12811, respectively (FIG. 4). When the light rosette centers are located upon corresponding points of the desired contour, the effects of the servo-voltages delivered to the integrators 68 and 78, through said lines, upon the deflection coils balance each other out so that the beam of tube 18 remains stationary. If one of said lines is blocked, however, and is unable to deliver its servo-voltages to integrator 68 or 78, as the case may be, its twin of opposite polarity charges the common integrator rapidly in such a manner that the deflection coils controlled by said integrator operate to move the beam in the direction opposite to that in which the voltages in the blocked line would have moved the beam had they not been opposed by the voltages of opposite polarity supplied by its twin. In accordance with the invention, the directional information obtained in section II of unit F is employed to block the normally open gate in the particular voltage supply line which opposes movement of the electron beam of the scanning tube in the direction closest to the desired contour. This causes an unbalance of the beam deflection control system which enables the voltages in the opposite line to force the beam unopposedly in the direction discovered to be closest to the contour; and as the beam is deflected in this manner and the centers of the light rosettes in moving in the direction of the desired contour deviate from said contourfor a contour will rarely if ever follow a straight line course the correctional voltages appearing in the other set of control lines operate to restore the beam continually in a direction at right angles to the forced movement of the beam to positions wherein the light rosettes are centered upon corresponding spots of the contour in the two diapositives. Thus, the light rosette centers follow the desired contour on the diapositives, and the beam of the scanning tube traces the desired contour in a continuous sequence of rosettes upon the screen of the scanning tube, and since the same control voltages are continually applied to the deflection coils 30x and 30y of the display tube 28, the desired contour is luminously traced in a continuous line upon the phosphor screen of said tube.

Reverting to FIGURE 5, the output of detector p which indicates that the contour extends more in East- West than in North-South direction-is simultaneously applied to two normally closed And gates E and 160W, respectively. Gate 160E may be opened to produce an output by the simultaneous appearance at its input side of a signal from detector 150p and a signal from the herein before described detector 156E which produces an output when the contour is closer to the x-axis in an eastern direction than in the western direction; and gate 160W may be opened to produce an output by the simultaneous appearance, at its input side, of a signal from detector 150p and a signal from the hereinbefore described detector 156W which produces an output when the contour is closer to the x-axis in a western than in an eastern direction. An output emerging from gate 160E means, therefore, that the contour extends in an East- West direction and is closer to the x-axis in eastern direction such as illustrated by the line 145 in FIGURE 7A. In accordance with the invention, this output is applied as a closing signal to the herein before mentioned normally open gate 124111 in the control line 12211 which delivers such servo-voltages to the integrator 68 as will move the beams of the cathode ray tubes along the x-axis in a negative direction, i.e. in a western direction. With gate 12411 closed, the integrator 68 is charged only through line 122p which supplies such servo-voltages as will shift the electron beam in an eastern direction, and as a result thereof, the deflection fields set up by coils 26x and 30x of tubes 18 and 28, respectively, under control of integrator 68 operate to shift the beams of said tubes in the eastern direction which is the direction found to be closest to the trend of the contour, and as the beams move in an eastern direction, correctional voltages continue to reach the integrator 78 which governs the deflection of said beams in the North-South direction so that the beams are continually servoed in the North-South direction to follow the desired contour.

On the other hand, an output produced by gate 160W means that the contour is closer to the x-axis in a western direction. Suchan output is applied as a closing signal to the hereinbefore mentioned normally open gate 124p in the control line 122;] which delivers such servo-voltages to the integrator 68 as will move the beams of the two cathode ray tubes in an eastern direction. Now, the integrator 68 is charged only with negative voltages causing the deflection coils 26x and 30x of the two cathode ray tubes to force the electron beams of said tubes in a western direction While the twin lines 126p and 12611 are left open to deliver such servo-voltages to the integrator 78 as will cause the beams of the two tubes to seek the desired contour continually in a North-South direction.

The output of detector 15011which appears only when the contour extends in a North-South direction rather than an East-West direction-is simultaneously applied to two normally closed parallel And gates 1661! and 1608. Gate 160N may be opened to produce an output by the simultaneous appearance, at its input side, of a sig nal from detector 15011 and a signal from detector 156N which passes a signal whenever the contour is closer to the y-axis in a northern direction than in a southern direction, as illustrated by line 147 in FIGURE 7B. The output of gate 160N is applied as a closing pulse to the normally open gate 12811 in the voltage supply line 12611 which delivers negative servo-voltages to the integrator 7 8 causing it to control current flow through the deflection coils 26y and 30y of the two cathode ray tubes in a manner that will shift their beams in a southern direction. As a result of closure of line 12611, the integrator 78 is charged through line 126p with positive voltages only, which is effective to force the electron beams of the two tubes in a northern direction, and with servo lines 122p and 12211 open and in operation, the beams are continually servoed in an East-West direction to cling to the discovered contour as they are forced to travel northwards.

Gate 1605 may be opened to produce an output by the simultaneous appearance, at the input side thereof, of a signal from detector 150n and a signal from detector 1565 which passes a signal only whenever the contour is closer to the y-axis in a southern direction than a northern direction. An output supplied by gate 1608 is applied as a closing pulse to the normally open control gate 128p in the servo-voltage supply line 126p which delivers such voltages to the integrator 78 as cause it to shift the beams of the two cathode ray tubes in a northern direction. With line 126p closed, the integrator 78 receives only negative servo-voltages through supply line 12611 with the result that the beams of the two cathode ray tubes are forced in a southern direction while being continually servoed in an East-West direction to remain on the contour.

As long as points representing the desired contour are clearly discernible in the examined diapositives, the correlation unit D of the apparatus of our invention generates in rapid succession many correlation-indicating pulses which are applied through line 121 (FIGURES 1 and 4) to, and open the gates 118p, 11811, 120p and 12011. As a result thereof the correctional voltages delivered to the integrators 68 and 78 and driver stages x and 80 gain substantial magnitude causing said driver stages to pass currents of such strength through the deflection coils 26x, 26y and 33x, 30y of the cathode ray tubes as will cause their electron beams to follow the discovered contour rapidly in the selected direction. On the other hand, when the searching light rosettes in following a contour on the diapositives reach areas where corresponding points of the contour are no longer easily discernible, the correlation unit D generates a lesser number of correlation pulses, the gates 118p, 11811, 120p and 12011 in the servo-voltage lines remain closed for increasingly longer intervals, and as a result thereof any servo-voltages passed through lines 122p, 12211, 126p and/or 12611- become weaker causing the contour following deflection of the beams in the two cathode ray tubes to slow down. This means that the contour-tracing beam proceeds more cantiously in areas that lack in clarity, and searches said areas more carefully and for longer periods of time; in other words, the apparatus of our invention act strikingly like a trained human stereo plotter operator.

Let us now revert to the hereinbefore mentioned attenuators 141x and 141 in the lines that lead from the twin gates 118p, 118n, and 120p, 12811, respectively, to the axis selecting integrator 142. When one of the inhibiting gates 124p, 124n, 128p or 12311 in the two twin sets of servo-voltage supply lines is closedto cause the electron beams of the two cathode ray tubes to follow the discovered contour, the voltages delivered to the axis selecting integrator 142 from the remaining three servovoltage supply lines do not longer represent the true state of affairs as far as the axis selecting performance of integrator 142 is concerned. Let it be recalled that voltages representing the existence of correlation in the proximity of the x-axis reach the integrator from twin gates 118p, 11811, and voltages representing the existence of correlation in the proximity of the y-axis reach the integrator from twin gates 120p, 12011. If the voltages emerging from one gate of one set of twin gates fail to reach the integrator 142 while both gates of the other set of twin gates continue to deliver their correlation indicating signals to said integrator, obviously the integrator does not receive all the information necessary to sense and indicate the trend of the examined contour correctly. It is to reduce the possibility of misoperation of the contour trend sensing arrangement under these conditions, that the repeatedly mentioned attenuators 141x and 1413 are placed in the common lines that lead from the set of twin gates 118p, 11811 and the set of twin gates 120p, 12011 respectively, to the integrator 14-2. In accordance with the invention, when one of the inhibiting gates 124p, 12411, 128p or 12811 in the two twin sets of servo-voltage supply lines 122]), 12211 and 126;), 12611 is closed, the attenuator 141x or 1413 in the common line leading from the unaffected set of servo-voltage supply lines to the integrator 142, is rendered effective to reduce the voltages delivered to said integrator from said unaffected set of servo-voltage su-p- 70 ply lines to about half their size. Thus, an approximation -Having again reference to FIGURE 5, the attenuators 141x and 141 are normally ineffective and pass all signals applied thereto without changing their amplitudes. However, they may be activated to reduce an applied sig nal to about half its size by application of an activating signal. In accordance with the invention, the output of detector 150p is applied through a line 151p as an activating signal to attenuator 141y, and the output of detector 15011 is applied through a line 15111 as an activating signal to the attenuator 141x. Whenever an output appears from detector 150p, this means that the desired contour extends closer to the xaxis than to the y-axis, and it means also that one of lines 122p, 122:1 will be blocked to cause the electron beams of the two cathode ray tubes to travel in an eastern or western direction, as the case may be. Accordingly, the output of detector 150p is employed to activate attenuator 141y to reduce the voltages that continue to reach the integrator 142 from twin lines 126p, 1261: to about half their size and thus compensate to an adequate degree for the unbalance between the signals of opposite polarity delivered to said integrator, that is introduced by blocking of the twin lines 122 12211.

Similarly, if an output appears from detector 15012 which indicates that the desired contour extends in North- South direction and which portends that one of the twin lines 126;), 126;: will be blockedline 15in applies such an output as an activating signal to the attenuator 141x to reduce to about half its size the amplitude of the signals reaching the axis-selecting integrator from servovoltage supply lines 122p and 12211.

In the above description of the construction and performance of the contour direction-sensing and following system of the present invention, it has been assumed for the purpose of simplifying the explanations, that the operations which lead to a decision along which axis and in which direction discovered contour is to be traced, start at the moment when the centers of the scanning light rosettes are located precisely upon the discovered contour. It will be understood that in actual practice these operations start as soon as any of the petals of the light rosettes reach and intersect the desired contour, and the decision "in which direction the contour is to be traced, depends therefore greatly upon the direction in which the rosettes approach the desired contour.

In searching areas around seemingly corresponding spots of a desired contour on the diapositives to find out whether two spots of identical light permeability are truly related spots that depict one and the same spot of the desired altitude in nature, and if so, to ascertain in which direction the discovered contour runs, it is necessary that the scanning light points in sweeping over said areas register immediately any discrepancies in the scanned areas so that generation of correlation-indicating pulses be immediately discontinued whenever such a discrepancy exists. We have found that when the scanning light points are swept over these areas in the pattern of a straight rosette, the contour sensing arrangement so far described is liable to miss discrepancies in the scanned areas that may exist in the regions where the petals of the rosette lie upon, or extend adjacent to, the y-axes of the scanned areas. This may best be understood by reference to FIG- URE 8 which depicts the critical areas of the searched diapositives and the paths'of the two searching light points as if they were superposed so that a single rosette 170 represents the trace of both light points. However, the two marks 172a and 174a drawn in full lines represent the reproductions of two spots of the scanned area on one diapositive and the partially overlapping marks 172b and 1741) drawn in broken lines represent the same spots on the other diapositive. The spot represented 'by the marks 174a and 174b is located close to the x-axis of the scanned .area, and the spot represented by the marks 172a and 17212 is located adjacent the y-axis thereof.

Let it be recalled that discrepancies, on two oriented diapositives, between marks depicting one and the same spot in nature can exist only in the direction of the x-axis of the diapositives because the observation points from which the photographs on the stereoscopically related diapositives were originally taken were spaced in this direction. Discrepancies in the location of corresponding marks on the diapositives in the direction of the y-axis cannot occur unless caused by irregularities in the manner in which the two photographs were taken at the two spaced observation points and the eifects of any such irregularities were carefully balanced out by the preparatory orientation of the diapositives prior to commencement of the contour searching operations. Reverting now to FIGURE 8 the partially overlapped marks 172a and 172b and 174a and 174b indicate a significant discrepancy of their location on the scanned diapositives in the direction of the x-axis and they cannot therefore represent spots of the desired contour. Let us now examine whether the scanning points of light are always capable of registering this fact. When said light points sweep over the marks 174a and 174k on the x-axis by tracing the rosette petals 176 upon the two diapositives the outputs of the photomultiplier tubes 20a and 20b behind the diapositives are bound to difler significantly if only for a 'brief moment, but when said light points sweep over the marks 172a and 172b adjacent to the y-axis of the diapositives by tracing the rosette petal 178 thereon the outputs of the photomultiplier tubes may not differ at all. This impairs the reliability of the intelligence produced by section II of unit F as to the trend of the desired contour, and may interfere with the ability of the correctional voltages generated by section I of unit F to locate the centers of the scanning light rosettes precisely upon the desired contour. To enable the scanning points of light to bring out clearly any discrepancies of the scanned areas in the direction of the x-axis whether they occur in the region of the x-axis or in the region of the y-axis of the scanned area, we impart a wobble in the direction of the x-axis to the scanning light points as they trace rosettes upon the scanned areas. The resultant configuration is illustrated at 180 in FIGURE 9. Said FIGURE 9 represents the same situation as FIGURE 8 and shows clearly that by imparting a horizontal" wobble, i.e. a wobble'in the direction of the x-axis, to the scanning points of light as they trace rosette petals upon the diapositives, discrepancies in the location of seemingly corresponding marks upon the diapositives in the direction of the x-axis are bound to afifect the output of the photomultiplier tubes behind the diapositives significantly whether the marks are located in the proximity of the x-axis or the y-axis. By virtue of the horizontal wobble, the two searching light points in tracing petals in synchronism upon the two diapositives, will produce different outputs from the photomultiplier tubes 20a and 20b even in situations such as represented by the horizontally displaced marks 172a and 172b near the y-axis of the rosettes as illustrated by the wobble petal 182 in FIGURE 9. In fact, we have found that the horizontal wobble imparted to the searching light rosettes is effective to provide improved discrimination in sensing discrepancies in situations such as represented by the marks 174a and 17'4b near the x axis of the rosettes. Thus, the danger that the apparatus of the invention may indicate correlation where in fact no correlation exists, is greatly minimized and the reliability and consistency of operation of the apparatus is greatly enhanced.

In practice the electron beam of the scanning tube 18 may be made to trace a luminous wobble rosette of the type illustrated in FIGURE 9 by applying the output of a sine wave generator or a triangular wave generator represented by the block 184 in unit B (FIGURE 2) to the driver stage 52x and the thus modulated output of said driver stage is delivered to the set of deflection coils 24x of the scanning tube 18. (In such an event the amplifiers x and 110y of unit F should be designed to act as filters whi h remove the Wobble com onent from the voltages applied to the two sets of twin gates 112p, 112:1 and 114p, 114n.) Alternatively, the output of a sine wave generator or a triangular wave generator may be applied to a special set of appropriately placed deflection coils on, or deflection plates in, the scanning tube. We have obtained excellent results by scanning with rosettes at a frequency of 100 rosettes per second wherein each rosette has 10 rosette petals and each petal 50 horizontal wobbles.

Summary In the apparatus of our invention, operation of unit B causes the electron beam of the scanning tube to trace a luminous wobble rosette of the type schematically illustrated in FIGURE 9 upon a spot of the phosphor screen thereof. The lenses 14a and 14b focus the light from said wobble rosette in a luminous wobble rosette pattern upon corresponding areas of the oriented diapositives 10a and 1012. By adjustment of the effective distance between the screen of the scanning tube and the plane of the diapositives the relative location of said wobble rosettes upon said diapositives corresponds to a desired altitude of the terrain depicted by said diapositives. The light from said rosettes which passes through the diapositives and reaches the photomultiplier tubes 22a and 22b, causes said tubes to produce output signals which differ as long as the light rosettes pass through unrelated areas of the two diapositives but which become increasingly similar when they pass through areas that depict one and the same point in nature that is of an altitude corresponding to the effective distance between the screen of the scanning tube and the plane of the diapositives. Manipulation of unit C makes it possible to shift the beam of the scanning tube in either the x or the y direction across the phosphor screen thereof which causes the light rosettes focused upon the diapositives to scan the diapositives in synchronism for such a spot in either the x or y direction. Continuous comparison of the outputs of the photomultiplier tubes 22a and 22b in unit D indicates When and where such a spot has been discovered. When the light rosettes in the diapositives reach areas whereat the output signals of the two multiplier tubes display near identity, they have encountered the reproductions of one and the same spot of the desired contour on the diapositives. In unit D, identical signals arriving simultaneously from the photomultiplier tubes are converted into pulses, and the appearance of a significant series of such pulses is employed to produce a correlation signal that is used to intensify the electron beam of the display tube 28 in unit E to an extent whereat it produces a luminous spot on the screen of said tube. Since unit C applies the same deflection fields to the beam of the display tube as it does to the beam of the scanning tube and the beams of both tubes therefore are always shifted in synchronism, said luminous spot depicts a spot of the desired contour. The same correlation signal that intensifies the electron beam of the dis-' play tube, is also employed to disable the beam shifting unit C, and since the beam position control voltages supplied by unit C are applied to the driver stages for the deflection coils 26x, 26y and 30x, 30y of both cathode ray tubes through integrators 68 and 78 that have a maximum discharge time, the charges built up in said integrators at the moment unit C is disabled, are effective to hold the beams of the two tubes in their momentary position of deflection.

At this moment unit F takes over and controls deflection of the beam of the scanning tube in a manner that will place the centers of the light rosettes precisely upon corresponding spots of the desired contour and shift them in one or the other direction in congruence with the desired contour so that the electron beam of the scanning tube actually traces the desired contour upon the screen of said tube in a continuous sequence of light rosettes. By applying the same deflection control voltages to the display tube, said tube provides an unobstructed view of the formation of the desired contour upon its phosphor screen in a simple continuous line. The described apparatus therefore traces a desired contour automatically in the most efficient manner upon the screen of the display tube, and by making photographs of said screen, a permanent record of the desired contour may readily be made. The effective distance between the light source producing screen of the scanning tube and the diapositives may then be varied to adjust the apparatus to a condition wherein it derives a contour of different altitude from the diapositives; and by repeating the automatic contour plotting process at a desired number of different adjustments of the distance between the screen of the scanning tube and the plane of the diapositives and making superposed photographic records of the contour lines appearing upon the screen of the display tube, contour maps of the terrain depicted upon the diapositives, that possess any desired number of contour lines of selected altitudes, may readily be produced by the apparatus of our invention in a minimum of time and without the element of error introduced by human intervention, in fact without need for human intervention other than the adjustment in the relative distance between the screen of the scanning tube and the plane of the scanned diapositives.

FIGURES 10 and 11 are reproductions of contour maps as actually obtained with the apparatus of the invention.

In describing the scanning operations involved in the performance of the apparatus of our invention, reference is made repeatedly to luminous points and rays of light. It will be understood by those skilled in the art that the radiations employed in scanning stereoscopically related photographs for desired contour lines need not necessarily lie in the visible spectrum. Therefore, whenever luminous points, rays of light and like terms are mentioned in the appended claims, these terms are understood to include radiations other than those of the visible spectrum.

While we have described our invention with the aid of a particular embodiment thereof, it will be understood that the invention is not limited to the specific circuit systems shown and described by way of example which may be departed from without departing from the scope and spirit of the invention.

We claim:

1. In an automatic contour plotter an arrangement comprising a cathode ray tube having a phosphor screen, means for projecting a beam of electrons onto said screen to produce a luminous point thereon, and means operable by the application of electric currents for deflecting said beam to shift the luminous point on said screen; means for scanning two stereoscopically related diapositives of a terrain including a pair of lenses placed to focus light rays from the luminous point in a predetermined relation upon said diapositives, and photosensitive devices exposed to the light rays focused upon said diapositives to produce output signals fluctuating in proportion to the transparency of the spots encountered by the light rays on said diapositives; first means for supplying such currents to said beam deflection means to shift said beam across said screen; means operative in response to correlation between the output signals of said photosensitive devices for generating signals indicative of the discovery of a spot of the desired contour on the diapositives; means operative in response to signals generated by said correlation signal generating means for disabling said first deflection current supply means; second means for supplying currents to said beam deflection means for deflecting said beam in a repetitive search pattern about a center point thereof to cause the light rays focused upon the diapositives to scan the areas around discovered contour spots; means utilizing said second deflection currents and the output of said correlation signal generating means for generating servo currents effective upon application to said beam deflection means to confine said beam to a position of deflection wherein the light rays focused upon the diapositives impinge upon corresponding spots of the desired contour; means for applying said servo currents to said beam deflection means; and means utilizing said second deflection currents and the outputs of said correlation signal generating means for sensing the direction of the desired contour and for curtailing the application of said servo currents to said beam deflection means so that the remaining servo currents shift the light point on the screen of said tube in such a manner that the light rays focused upon the diapositives follow corresponding contours of said diapositives.

2. In an automatic contour plotter an arrangement comprising a cathode ray tube having a phosphor screen, means for projecting a beam of electrons onto said screen to produce a luminous point thereon, and means operable by the application of electric currents for deflecting said beam to shift the luminous point on said screen; means for scanning two stereoscopically related diapositives of a terrain including a pair of lenses placed to focus light rays from the luminous point in a predetermined relation upon said diapositives, and photosensitive devices exposed to the light rays focused upon said diapositives to produce output signals fluctuating in proportion to the transparency of the spots encountered by the light rays on said diapositives; first means for supplying such currents to said beam deflections means to shift said beam across said screen; means operative in response to correlation between the output signals of said photosensitive devices for generating signals indicative of the discovery of a spot of the desired contour on the diapositives; means operative in response to signals generated by said correlation signal generating means for disabling said first deflection current supply means; second means for supplying currents to said beam deflection means for deflecting said beam in a Wobble rosette pattern about a center point thereof to cause the light rays focused upon the diapositives to scan the areas around discovered contour spots; means utilizing said second deflection currents and controlled by the output of said correlation signal generating means for generating servo currents effective upon application to said beam deflection means vto confine said beam to a position of deflection wherein the light rays focused upon the diapositives impinge upon corresponding spots of the desired contour; means for applying said servo currents to said beam deflection means; and means utilizing said second deflection currents and controlled by the output of said correlation signal generating means for sensing the direction of the desired contour and for curtailing the application of said servo currents to said beam deflection means so that the remaining servo currents shift the light point on the screen of said tube in such a manner that the light rays focused upon the diapositives follow corresponding contour lines of said diapositives.

3. An automatic contour plotter comprising a first cathode ray tube having a phosphor screen, means for projecting a beam of electrons onto said screen to produce a luminous point thereon, and means operable by the application of electric currents for deflecting said beam to shift the luminous point on said screen; means for scanning two stereoscopically related diapositives of a terrain including a pair of lenses placed to focus light rays from the luminous point in a predetermined relation upon said diapositives, and photosensitive devices exposed to the light rays focused upon said diapositives to produce output signals fluctuating in proportion to the transparency of the spots encountered by the light rays on said diapositives; means for supplying such currents to said beam deflection means to shift said beam across said screen in a repetitive pattern continuallyintersecting a center point thereof to cause the light rays focused upon the diapositives to scan the areas around discovered contour spots; means operative in response to correlation between the output signals of said photosensitive devices for generating signals indicative of the discovery of a spot of the desired contour on the diapositives; means utilizing said deflection currents and controlled by the output of said correlation signal generating means for generating servo currents effective upon application to said beam deflection means to confine said beam to a position of deflection wherein the light rays focused upon the diapositives impinge upon corresponding spots of the desired contour; means for applying said servo currents to said beam deflection means; means utilizing said deflection currents and controlled by the output of said correlation signal generating means for sensing the direction of the desired contour and for curtailing the application of said servo currents to said beam deflection means in a manner effective to cause the remaining servo currents to shift the light point on the screen of said tube in such a manner that the light rays focused upon the diapositives follow corresponding contour lines on said diapositives; a second cathode ray tube having a phosphor screen, means for projecting an electron beam onto said screen, and means operable by the application of electric currents for deflecting said beam; and means for applying said servo currents to the beam deflection means of said second tube in the same manner as the beam deflection means of said first tube to cause the electron beam of said second tube to trace the desired contour luminously upon the phosphor screen thereof.

4. An automatic contour plotter comprising a first cathode ray tube having a phosphor screen, means for projecting a beam of electrons onto said screen to produce a luminous point thereon, and means operable by the application of electric currents for deflecting said beam to shift the luminous point on said screen; means for scanning two stereoscopically related diapositives of a terrain including a pair of lenses placed to focus light rays from the luminous point in a predetermined relation upon said diapositives, and photosensitive devices exposed to the light rays focused upon said diapositives to produce output signals fluctuating in proportion to the transparency of the spots encountered by the light rays on said diapositives; first means for supplying such currents to said beam deflection means to shift said beam across said screen; means operative in response to correlation between the output signals of said photosensitive devices forgenerating signals indicative of the discovery of a spotof v the desired contour on the diapositives; means operative in response to signals generated by said correlation signal generating means for disabling said first deflection current supply means; second means for supplying currents to said beam deflection means for deflecting said beam in a repetitive search pattern about a center, point thereof to cause the light focussed on the diapositives to scan the areas around discovered contour spots, means utilizing said second deflection currents and the output of said correlation signal generating means for generating servo currents effective upon application to said beam contour; means for applying said servo currents to said beam deflection means; means utilizing said second de-t flection currents and the output of said correlation signal generating means for sensing the direction of the desired contour and for curtailing the application of said servo currents to said beam deflection means in a manner effective to cause the remaining servo currents to shift thelight point on the screen of said tube in such a manner; that the light rays focused upon the diapositives follow corresponding contour lines on said diapositives; a second cathode ray tube having a phosphor screen, means for projecting an electron beam onto said screen, meansfor controlling the intensity of said beam, and means operable by the application of electric currents for deflecting said beam; means for applying the output of said correlation signal generating means to said beam intensity control means of said second tube to increase the intensity of the beam of said second tube and thus indicate luminously a discovered contour spot on the screen of said second tube; and means for applying said servo currents to the beam deflection means of said second tube in the same manner as to the beam deflection means of said first tube to cause the electron beam of said second tube to trace the desired contour luminously upon the phosphor screen of said second tube.

5. Apparatus according to claim 4 wherein said second deflection current supply means is arranged to deflect the electron beam of said first cathode ray tube in the manner of a rosette Whose petals display a horizontal wobble.

6. In an automatic contour plotter an arrangement comprising means for scanning two stereoscopically related photographs of a terrain including a cathode ray tube having a phosphor screen, means for projecting an electron beam onto said screen to produce a luminous point thereon, means for directing light rays from said luminous point in a predetermined relation onto said photographs, means operable by the application of currents for deflecting the beam along an axis, means for delivering deflection currents having positive and negative phases to said deflection means to deflect the beam along said axis in a positive and negative direction, and photosensitive means exposed to the light rays directed onto said photographs to produce output signals varying in proportion to the density of the spots on the photographs encountered by said light rays; means operative in response to correlation between the output signals of said photosensitive devices to generate signal-s indicative of impingement of the light rays upon corresponding spots of the desired contour on the photographs; means for generating servo signals effective upon application to said beam deflection means to shift the beam in a direction wherein the light rays directed onto the photographs produce output signals from said correlation signal generating means; contour trend sensing means including means for comparing the incidence of correlation during deflection of the beam along the axis in a positive and a negative direction to determine whether the desired contour extends closer to the axis in the positive or the negative direction; and means controlled by said contour trend sensing means for unbalancing application, to said beam deflection means, of the servo signals in such a manner as to shift the beam in the direction of greater correlation incidence.

7. In an automatic contour plotter an arrangement comprising means for scanning two stereoscopically related diapositives of a terrain including a cathode ray tube having a phosphor screen, means for projecting an electron beam onto said screen to produce a luminous point thereon, means for directing light rays from said luminous point in a predetermined relation onto said diapositives, means operable by the application of currents for deflecting the beam along different axes, means for delivering deflection currents having positive and negative phases to said deflection means to deflect the beam along said axes in a positive and negative direction, and photosensitive means exposed to the light rays directed onto said diapositives to produce output signals varying in proportion to the transparency of the spots on the diapositives encountered by said light rays; means operative in response to correlation between the output signals of said photosensitive dew'ces to generate signals indicative of impingement of the light rays upon corresponding spots of the desired contour on the diapositives; means for generating servo signals effective upon application to said beam deflection means to shift the beam in a direction wherein the light rays directed onto the diapositives produce output signals from said correlation signal generating means; contour trend sensing means including means for comparing the incidence of correlation during deflection of the beam in the direction of said axes to determine along which axis more correlation occurs, and means for comparing the incidence of correlation during the deflection of the beam along each axis in a positive and a negative direction to determine whether the desired contour extends closer to an axis in the positive or the negative direction; and means activated by said contour trend sensing means for blocking application, to said beam deflection means, of the servo signals tending to shift the beam in a direction opposite to the direction of maximum correlation incidence.

8. In an automatic contour plotter an arrangement comprising means for scanning two stereoscopically related diapositives of a terrain including a cathode ray tube having a phosphor screen, means for projecting an electron beam onto said screen to produce a luminous point thereon, lenses placed to direct light rays from said luminous point in a predetermined relation onto said diapositives, means operable by the application of currents for deflecting the beam along the x-axis and the y-axis of a Cartesian system, means for delivering deflection currents to said deflection means to deflect the beam along said xand y-axes, and photosensitive means exposed to the light rays directed onto said diapositives to produce output signals Varying in proportion to the transparency of the spots on the diapositives encountered by said light rays; means operative in response to correlation between the output signals of said photosensitive devices to generate signals indicative of impingement of the light rays upon corresponding spots of the desired contour on the diapositives; means utilizing said deflection currents and controlled by said correlation indicating signals for generating servo signals effective upon application to said beam deflection means to shift the beam in a direction wherein the light rays directed onto the diapositives produce output signals from said correlation signal generating means; contour trend sensing means including an integrator for comparing the incidence of correlation during deflection of the beam in the direction of the x-axis and the y-axis to determine along which axis more correlation occurs and thus sense whether the desired contour extends closer to said x-axis or said yaxis; means activated by said contour trend sensing means for unbalancing application, to said beam deflection means, of the servo signals in such a manner as to shift the beam in the direction of maximum correlation incidence.

9. In an automatic contour plotter an arrangement comprising means for scanning two stereoscopically related diapositives of a terrain including a cathode ray tube having a phosphor screen, means for projecting an electron beam onto said screen to produce a luminous point thereon, lenses placed to direct light rays from said luminous point in a predetermined relation onto said diapositives, means operable by the application of cur rents for deflecting the beam along the x-axis and the yaxis of a Cartesian system, means for delivering deflection currents having positive and negative phases to said deflection means to deflect the beam cyclically along said xand y-axes in a positive and negative direction, and photosensitive means exposed to the light rays directed onto said diapositives to produce output signals varying in proportion to the transparency of the spots on the diapositives encountered by said light rays; means operative in response to correlation between the output signals of said photosensitive devices to generate signals indicative of impingement of the light rays upon corresponding spots of the desired contour on the diapositives; means utilizing said deflection currents and controlled by said correlation indicating signals for generating servo signals effective upon application to said beam deflection means to shift the beam in a direction wherein the light rays directed onto the diapositives produce output signals from said correlation signal generating means; contour trend sensing means including a first integrator for comparing the incidence of correlation during deflection of the beam in the direction of said x-axis and said y-axis to determine along Which axis more correlation occurs and thus sense whether the desired contour extends closer to said x-axis or said y-axis, and second integrators for comparing the incidence of correlation during the deflection of the beam along each axis in a positive and a negative direction to determine whether the desired contour extends closer to an axis in the positive or the negative direction; and means activated by said contour trend sensing means for blocking application, to said beam deflection means, of the servo signals tending to shift the beam in a direction opposite to the direction of maximum correlation incidence.

10. Apparatus according to claim 9 wherein said deflection current supply means is arranged to deflect the electron beam of said cathode ray tube cyclically in the 24 manner of a rosette whose petals display a horizontal wobble.

References Cited UNITED STATES PATENTS 2,679,636 5/1954 'Hillyer' 8814 X 2,912,761 11/1959 Woodward et al. 3,145,303 6/1964 Hobrough 8824 3,173,015 3/1965 Moneypenney et al 88-14 3,246,560 4/1966 Birnbaum et a1 88-14 JEWELL H. PEDERSEN, Primary Examiner.

F. SHOON, O. B. CHEW, Assistant Examiners. 

1. IN AN AUTOMATIC CONTOUR PLOTTER AN ARRANGEMENT COMPRISING A CATHODE RAY TUBE HAVING A PHOSPHOR SCREEN, MEANS FOR PROJECTING A BEAM OF ELECTRONS ONTO SAID SCREEN TO PRODUCE A LUMINOUS POINT THEREON, AND MEANS OPERABLE BY THE APPLICATION OF ELECTRIC CURRENTS FOR DEFLECTING SAID BEAM TO SHIFT THE LUMINOUS POINT ON SAID SCREEN; MEANS FOR SCANNING TWO STEREOSCOPICALLY RELATED DIAPOSITIVES OF A TERRAIN INCLUDING A PAIR OF LENSES PLACED TO FOCUS LIGHT RAYS FROM THE LUMINOUS POINT IN A PREDETERMINED RELATION UPON SAID DIAPOSITIVES, AND PHOTOSENSITIVE DEVICES EXPOSED TO THE LIGHT RAYS FOCUSED UPON SAID DIAPOSITIVES TO PRODUCE OUTPUT SIGNALS FLUCTUATING IN PROPORTION TO THE TRANSPARENCY OF THE SPOTS ENCOUNTERED BY THE LIGHT RAYS ON SAID DIAPOSITIVES; FIRST MEANS FOR SUPPLYING SUCH CURRENTS TO SAID BEAM DEFLECTION MEANS TO SHIFT SAID BEAM ACROSS SAID SCREEN; MEANS OPERATIVE IN RESPONSE TO CORRELATION BETWEEN THE OUTPUT SIGNALS OF SAID PHOTOSENSITIVE DEVICES FOR GENERATING SIGNALS INDICATIVE OF THE DISCOVERY OF A SPOT OF THE DESIRED CONTOUR ON THE DIAPOSITIVES; MEANS OPERATIVE IN RESPONSE TO SIGNALS GENERATED BY SAID CORRELATION SIGNAL GENERATING MEANS FOR DISABLING SAID FIRST DEFLECTION CURRENT SUPPLY MEANS; SECOND MEANS FOR SUPPLYING CURRENTS TO SAID BEAM DEFLECTION MEANS FOR DEFLECTING SAID BEAM IN A REPETITIVE SEARCH PATTERN ABOUT A CENTER POINT THEREOF TO CAUSE THE LIGHT RAYS FOCUSED UPON THE DIAPOSITIVES TO SCAN THE AREAS AROUND DISCOVERED CONTOUR SPOTS; MEANS UTILIZING SAID SECOND DEFLECTION CURRENTS AND THE OUTPUT OF SAID CORRELATION SIGNAL GENERATING MEANS FOR GENERATING SERVO CURRENTS EFFECTIVE UPON APPLICATION TO SAID BEAM DEFLECTION MEANS TO CONFINE SAID BEAM TO A POSITION OF DEFLECTION WHEREIN THE LIGHT RAYS FOCUSED UPON THE DIAPOSITIVES IMPINGE UPON CORRESPONDING SPOTS OF THE DESIRED CONTOUR; MEANS FOR APPLYING SAID SERVO CURRENTS TO SAID BEAM DEFLECTION MEANS; AND MEANS UTILIZING SAID SECOND DEFLECTION CURRENTS AND THE OUTPUTS OF SAID CORRELATION SIGNAL GENERATING MEANS FOR SENSING THE DIRECTION OF THE DESIRED CONTOUR AND FOR CURTAILING THE APPLICATION OF SAID SERVO CURRENTS TO SAID BEAM DEFLECTION MEANS SO THAT THE REMAINING SERVO CURRENTS SHIFT THE LIGHT POINT ON THE SCREEN OF SAID TUBE IN SUCH A MANNER THAT THE LIGHT RAYS FOCUSED UPON THE DIAPOSITIVES FOLLOW CORRESPONDING CONTOURS OF SAID DIAPOSITIVES. 